I alternate wool covers so they have a chance to dry. As long as they've dried and weren't pooped on, I'll re-use them the same day. If you want to use wool frequently, you may want more than two covers because eventually you're going to need to lanolize and they can take a while to dry.
Re: Summer wool shorties?
DS1: 10/2005 DS2: 01/2007 DS3: 09/2010